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1. Field of the Invention
The present invention generally relates to medical devices, and more particularly relates to devices for diagnosing various cardiac conditions.
2. Description of the Prior Art
It is well known in the prior art to design and build apparatus for the diagnosis of various cardiac disorders. Certain symptomatic chronic conditions are quite easily identified and diagnosed. However, various intermittent conduction disorders may require substantial diagnostic testing and analysis.
Some of the most difficult diagnoses are associated with intermittent conduction conditions. Typically, such disorders may cause tachycardia ( i.e.,too fast heart beat), as well as bradycardia (i.e., too slow heart beat), and potentially even cardiac arrest (i.e., no heart beat) and fibrillation (i.e., uncontrolled super fast heat activity). These conditions range from extremely serious to fatal. Therefore, it is important to diagnose and treat the underlying pathology before any of these symptoms appear in environments not having emergency treatment resources.
One current approach, which is particularly useful in the diagnosis of these intermittent cardiac conduction disorders, is electrophysiological (EP) mapping. In accordance with this technique, the patient is taken to a catheter laboratory in which catheters are passed into the interior of the heart. These electrically conductive catheters permit instruments to analyze and record the electrical activity at points within the myocardium which are in contact with one or more electrodes of the catheter. In a typical diagnostic catheter, a single electrode is positioned at the distal end of the catheter. Each repositioning of the distal end of the catheter permits measurement of electrical activity at another myocardial location. In another version, multiple electrodes are located in a basket-like arrangement that expands inside the heart to bring the electrodes into contact with the myocardium. The electrical activity of the myocardium is xe2x80x9cmappedxe2x80x9d by the recording of electrical activity as a function of electrode position in contact with the myocardium.
Electrophysiological mapping permits the diagnostician to view each physical location within the myocardium exhibiting improper and suspect electrical activity. Following diagnosis, typical treatments include: management with medication; ablation of improperly functioning myocardial tissue; implantation of a medical device to treat conduction deficiencies (e.g., pacemaker, cardioverter, etc.); more invasive surgical procedure; or a combination of these procedures.
Typically, sensing electrodes are made from metal rings or cylindrical plugs made from biocompatible grade metal alloys like platinum and stainless steel. Some designs use a sintered metal made from micron sized metal particles which are hydraulically pressed together and then fired to obtain the requisite strength.
A particular problem with electrophysiological mapping catheters arises because of the low level of the electrical signals derived from the contact between the myocardium and a relative small geometry electrode. One solution to low electrical signals from a sensing electrode that is used for long-term, chronic sensing and stimulation is to increase the size of the electrode in contact with the myocardium. However, increasing the size of the electrode for an electrophysiological mapping catheter creates a greater sensing footprint on the myocardial surface, which decreases the resolution of the mapping process.
The present invention overcomes many of the disadvantages found in the prior art by providing a method of and apparatus for an electrophysiological catheter that increases the signal strength derived during the mapping process without increasing the electrode footprint in contact with the myocardial tissue. The technique is useful with both ring type and cylindrical plug type electrode constructions. It may be utilized with virtually any suitable electrode material or electrode configuration.
In accordance with the preferred mode of the present invention, a coating is applied to the exterior surface of the electrode structure to greatly increase the effective surface contact area without appreciably changing the contact footprint. However, unlike electrodes for chronic sensing and stimulation, this coating is selected to optimize acute sensing, rather than enhance chronic positional stability via tissue ingrowth or improved stimulation current densities.
Preferably, the coating is of a different material from the electrode structure. Titanium nitride (TiN) is the preferred material. The coating is applied at a thickness of from several angstroms to several millimeters. The coated surface may be continuous or discrete.
This coated surface layer creates a micro texturing which substantially increases the effective surface area in direct proximity to the tissue. The enhanced surface contact produces a sharper sensed signal due to decreased polarization thereby reducing the amount of capacitive coupling and increasing the signal-to-noise ratio. However, this larger effective surface contact area retains essentially the same footprint as the uncoated electrode. Therefore, the resolution of the mapping process is not adversely effected.